The present invention relates to manufacturing a solid electrolytic capacitor having a valve metal on which an anodized film is formed as an anode.
In conventional methods of manufacturing solid electrolytic capacitors (hereafter referred to as xe2x80x9csolid capacitorsxe2x80x9d), an anodized film, base layer, conductive polymer layer, and cathode conductor layer are successively formed on the surface of a foil or fine powder sintered body of valve metal which becomes an anode, that is a positive electrode. After lead wires are connected to a capacitor element, it is molded with a packaging resin to complete the solid capacitor. In general, a MnO2 layer is used as a base layer in this series of manufacturing processes. As the MnO2 layer is usually formed by thermally decomposing manganese nitrate, the anodized film is significantly damaged when aluminum is used as the anode, causing large leak current in the completed solid capacitors.
For solving the above problem, Japanese Laid-open Patents Nos. S63-181310 and H2-260516 disclose re-anodization in electrolytic solution after forming the conductive polymer layer. Japanese Laid-open Patent No. H3-178117 also discloses a method of forming a conductive polymer layer on the MnO2layer after adhering an insulating resist tape on the anodized film to separate a cathode, that is a negative electrode and anode, and then forming the MnO2 layer by thermal decomposition.
These conventional methods disclosed in Japanese Laid-open Patent Nos. S63-181310 and H2-260516 involve re-anodization after forming a conductive polymer layer in the electrolytic solution. The electrolytic solution is thus difficult to sufficiently provide on the anodized film, making this process insufficient for fully repairing any damage to the anodized film. In addition, the conductive polymer layer sometimes degrades under some anodizing conditions, resulting in unsatisfactory impedance characteristics.
The conventional method disclosed in the Japanese Laid-open Patent No. H3-178117 requires re-anodization after formation of the MnO2 layer by thermal decomposition. Otherwise, the significantly damaged anodized film permits the flow of large leak current. In addition, even if re-anodization is implemented, adhesives on the resist tape seep out and interfere with the repairability of defective portions of the anodized film near the resist tape.
The present invention addresses the above disadvantages of conventional methods, and provides a method of manufacturing solid electrolytic capacitors with less leak current and good impedance characteristics.
The method of manufacturing solid capacitors of the present invention comprises:
forming an anodized film on the surface of a valve metal anode body;
separating a cathode part and anode part on the anodized film;
forming a base layer for a solid electrolyte layer on the anodized film;
immersing a capacitor element on which the base layer is formed into an organic polar solvent or solution thereof;
removing the capacitor element from the organic polar solvent or solution thereof, and immersing it in an electrolytic solution before the solvent or its solution dries up, for re-anodization; and
forming a solid electrolyte layer and cathode conductor layer on the base layer.
Furthermore, the method of manufacturing solid capacitors of the present invention comprises:
forming an anodized film on the surface of the anode which comprises a valve metal;
adhering an insulating resist tape for separating a cathode part and an anode part on the anodized film;
immersing a capacitor element on which the insulating resist tape is adhered into a solution comprising dissolved manganese salts;
removing the capacitor element from the solution and forming a MnO2 layer by thermally decomposing the manganese salts on the capacitor element;
immersing the capacitor element in an organic polar solvent or solution thereof;
removing it from the organic polar solvent or solution thereof and immersing it in an electrolytic solution, before the solvent or solution thereof dries, for re-anodization; and
forming a solid electrolyte layer and cathode conductor layer on the base layer.
Accordingly, wettability of the cathode in the re-anodization process improves, and small defects on the anodized film can be repaired. The present invention thus provides solid capacitors with less leak current.